Word of advice: don't do what the author has done. He has gone from one extreme (categorizing all notes obsessively) to the other extreme (wiping all notes, to start fresh).
The answer, as usual, is in the middle: keep all notes, archived. Feel free to restart old projects/ideas by archiving old projects to old/2024/legacy, and starting with a fresh page/folder, occasionally looking back at archived notes, if needed.